Bearings and other shaft mountable members are used in a variety of devices including turbochargers. In a conventional turbocharger, a turbine and a compressor are positioned at opposite ends of a center housing, and a shaft extends through the center housing to connect the turbine and compressor. The shaft is rotatably supported within the center housing by one or more bearings. The center housing typically defines a passage defining an inlet and outlet for circulating oil to and from the bearings. Radially extending holes can be provided in the bearings or other members mounted on the shaft, such as a spacer disposed between two bearings. The oil can flow through or between the bearings or other shaft mounted members and thereby circulate from the inlet of the housing to the shaft, and then back through or between the bearings or other shaft mounted members to the outlet. The oil provides lubrication between the various parts, e.g., between the rotating shaft and the bearings and other members thereon. The oil can also function as a coolant to convect thermal energy away from the parts.
The flow of oil radially between the adjacent surfaces of the bearings and other shaft mounted members provides lubrication and cooling to the adjacent members and increases the circulation of oil to the shaft. However, axial movement of the shaft mounted members can reduce the space between the adjacent members and prevent circulation of the oil therebetween. Such axial motion of the shaft mounted members can occur due to dynamic or hydraulic forces translated through the turbine, compressor, shaft, and the like. In addition, the circulation of the oil can be reduced if the pressure or temperature of the oil varies, as can occur during typical operation. As a result of the decrease in oil circulation, the members and/or the oil can become hotter, thereby reducing the effectiveness of the oil and increasing the wear on the parts.
In some cases, grooves can be provided on the axial face of the bearing for generating an axial force between the bearing and the adjacent member. For example, U.S. Pat. No. 6,017,184 describes a bearing that is pinned to a bearing housing so the bearing system does not rotate. Thrust surfaces of the bearing are contoured to include radial grooves, lower flats, ramps, and upper lands. Oil is circulated radially through the grooves between the bearing and an adjacent member such that the oil causes a thrust force between the bearing and the adjacent member. In other conventional turbochargers, the grooves can be provided without ramps or other contours to achieve similar thrusting capacity between the members. Such grooved bearings provide improved oil circulation, but also complicate the manufacture of the bearings and/or the turbochargers, thereby increasing the cost. Further, the thrust generated by such bearings can be unnecessary or undesirable for particular applications.
There exists a need for an improved shaft member, such as a bearing, shaft, or shaft mountable member, for providing circulation of oil radially. Preferably, the shaft member should provide circulation under various conditions, including axial movement of the shaft or shaft mounted members and varying temperature or pressure of the oil. The shaft member should also enable circulation of the oil without significant generation of thrust between the shaft member and adjacent shaft mounted members.